Rejected swain's temperature rising (6)
I believe the answer is:
revolt
'rising' is the definition.
(rising can mean a revolt or rebellion)
'rejected swain's temperature' is the wordplay.
'rejected' says the letters should be written backwards.
'swain' becomes 'lover' (archaic term for a lover).
'temperature' becomes 't' (abbreviation).
'lover' written backwards gives 'revol'.
'revol'+'t'='REVOLT'
(Other definitions for revolt that I've seen before include "Rebel or disgust" , "Rising" , "'Uprising, rebellion (6)'" , "Don't hurry" , "Rebel; rebellion" .)